Hello,
I had a question about slander and was not sure if I would have a case or not. I recently started a new job, and it was apparent right from the start that my supervisor did not like me and was threatened by my presence. I had held the same job that she currently the had at another location and moved closer to home and I was her assistant. I have now had people approaching me at work and telling me some of the things she has been saying about me and they are total lies. Things about me stealing and trying to get other employees fired so I could have my old employees take their place. Just things that are not true at all. I have found out that she has talked to everyone that will listen and just spread these lies. Now most of the staff in our department does not like me and I have been treated like an outcast. It got to the point that I have now stepped down as her assistant and told my District Manager about it and she has not even addressed it! I am not sure if I have anything here but any advice would be appreciated. Thank you

First you need proof of what she has said. Next you need to show how these statements damaged you.

Before I try suing, I would have a talk with her boss and explain what's going on.

Here is a link that may help you to understand the complex nature of harassment in the workplace.
Legal Remedies for Harassment in the Workplace | Legal > Labor & Employment Law from AllBusiness.com (http://www.allbusiness.com/human-resources/workplace-health-safety/12470-1.html)

I have talked to her boss, and she just told the boss more lies about me, like that I was not even doing my job, which is a lie, and I can prove. So I have had no resolution at this level, and the problem is that her boss is the district manager, so there is no one above her that I can take this to.

Talk to the DM again and bring your proof. Catch her in at least one lie and you may get action.